The present invention relates in general to a laser transmitter, and, more particularly, to a system for distinguishing true target reflections from ghost target reflections so as to adjust the orientation of a plane of laser light as defined by the true target reflections.
Laser light systems have been employed in numerous surveying and construction applications. In one such system, a laser light transmitting device provides a rotating laser beam which establishes a reference plane. Typically, the rotating laser beam is used to provide a continuous plane of light that creates either a constant horizontal bench mark of elevation or a selected plane over an entire work area. The laser light is either detected by the naked eye or by one or more laser beam detectors, placed at considerable distances from the transmitting device. Various construction tasks are performed based on the visual perception of the laser light, while the detectors are used to intercept the rotating laser beam and determine a proper elevation and grade at selected points throughout the work area.
In the laser light transmitting device, the plane of light is produced by projecting the beam generally upward and then deflecting the beam ninety degrees within a pentaprism or penta-mirror assembly. The pentaprism assembly is rotated about a vertical axis within the transmitting device to cause the beam to rotate and define the reference plane. The laser transmitting device may be adjusted so that the orientation of the rotating beam of light defines a desired plane with respect to a generally horizontal or vertical plane.
Retroreflective targets may be positioned at desired locations to define the desired plane through which the beam of light is rotated. The beam of light is reflected from the retroreflective targets and transmitted back to the transmitting device. The transmitting device determines the location of the retroreflective targets and adjusts the orientation of the rotating beam of light in response to the light reflected from the retroreflective targets. However, reflective surfaces adjacent to the retroreflective targets, such as shiny floors or glossy walls, tend to create a ghost or mirror image of the retroreflective targets. These ghosts images may confuse the transmitting device thereby affecting the accuracy of the adjustments necessary to align the rotating laser beam so that it is oriented in the desired plane.
Accordingly, there is a need in the art for an automatic and accurate system for distinguishing true target reflections from ghost target reflections so as to enable the orientation of a plane of laser light to be adjusted accurately based on the true target reflections. Preferably, such a system would be inexpensive and easy to operate.